A liquid crystal display device (hereinafter, referred to as an “LCD device”) usually includes a liquid crystal panel including a liquid crystal component injected between two transparent substrates, and an optical film. As an optical film, a polarizing film, a retardation film or a brightness-enhancing film may be used, and to laminate such an optical film or attach the optical film to an adherent such as the liquid crystal panel, a pressure-sensitive adhesive for an optical film is widely used. As a pressure-sensitive adhesive, an acrylic polymer, a rubber, a urethane resin, a silicon resin or an ethylene vinyl acetate(EVA) resin may be used, and particularly, as a pressure-sensitive adhesive for an optical film such as a polarizing plate, an acrylic copolymer having excellent transparency and high resistance to oxidation or yellowing is generally used.
Main physical properties required for a pressure-sensitive adhesive composition for an optical film include cohesive strength, pressure-sensitive adhesive strength, reworkability, low light leakage and stress relaxation. In Patent documents 1 to 3, a pressure-sensitive adhesive composition for achieving the above physical properties is suggested.